Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display Intracellular fluid Channel proteins Lipid bilayer Open ion channel Closed ion channel Extracellular fluid The opening and closing of ion channels results from conformational changes in integral proteins Discovering the factors that cause these changes is key to understanding excitable cells.The opening and closing of ion channels results from conformational changes in integral proteins. Discovering the factors that cause these changes is key to understanding excitable cells